The present invention relates to a printing medium discharge apparatus used in an ink jet printer, the printer printing a desired image by ink jet on a printing medium while it is held on a rotary drum, and the discharge apparatus discharging the printing medium, on which the desired image have been printed, from the rotary drum.
As personal computers have widely been marketed, their associated color printers are demanded for commercial use. Such conventional color printers are classified into serial, parallel, and line types depending on the mode of printing equipment.
A serial printing equipment includes a printing head having a plurality of ink jet nozzles for ejection of different colors (namely, yellow, magenta, cyan, and black). A conventional color printer provided with the serial printing equipment permits a printing medium such as a sheet of paper of a given size to be conveyed at equal intervals of a pitch in a predetermined direction. During the conveying, the printing head performs reciprocating motions over a surface of the printing medium at a right angle to the conveying direction of the printing medium. The printing head while traveling over the printing medium applies jets of specific inks to the surface of the printing medium at a given location in the reciprocating motion. As the printing head repeats application of the inks to the surface of the printing medium along the conveying direction, a desired image of the inks (which may include characters, numerals, symbols, etc.) is printed in a given area on the surface of the printing medium. The construction of such a conventional color printer provided with the serial printing equipment is well known. The conventional color printer has a printing head which can easily be fabricated and its overall arrangement is relatively simple, thus minimizing the size and lowering the cost. However, the conventional color printer has some disadvantages that the printing head is slow in the speed of printing action and produces a considerable degree of noise, hence being hardly suited for the business use which requires production of a large number of prints in a shorter duration of time with less sounds.
A conventional color printer provided with the parallel printing equipment allows a printing medium such as a sheet of paper of a given size to be conveyed at a specific speed in a predetermined direction under a plurality of printing units which are arranged at intervals of a given distance along the conveying direction. The printing units are parallel to each other extending at a right angle to the conveying direction between both sides of the printing medium. While the printing medium is conveyed at the specific speed in the conveying direction, different colors (namely, yellow, magenta, cyan, and black) are applied by their respective printing units to print an image on the printing medium. Each of the printing units comprises a photosensitive drum and a static charger, an exposer, a toner developer, a transfer device, a cleaner, and a discharger mounted about the photosensitive drum. The printing unit of this arrangement is known as used in a plain paper copier (PPC). The conventional color printer of this type is quiet during the printing action and high in the printing speed, and thus produces a large number of prints within a short period of time and can thus be suited for business use. However, the conventional color printer provided with the parallel printing equipment includes two or more of the printing units which are expensive and its construction is not simple, thus increasing the cost of production as well as the overall size.
A color printer provided with the line type printing equipment also permits a printing medium such as a sheet of paper of a given size to be conveyed at a specific speed in a predetermined direction under a plurality of printing head which are arranged at intervals of a given distance along the conveying direction. The printing heads are parallel to each other extending at a right angle to the conveying direction between both sides of the printing medium. Each of the printing heads includes a plurality of ink jet nozzles for ejection of one of different color inks (namely, yellow, magenta, cyan, and black). The ink jet nozzles on the printing head are aligned in a row extending at a right angle to the conveying direction between two sides of the printing medium. While the printing medium is conveyed at the specific speed in the conveying direction, the colors are applied by their respective printing heads.
As compared with the serial printing equipment, the line type printing equipment has the following advantages and disadvantage.
The printing head in the line type printing equipment has a greater number of the ink jet nozzles than that in the serial printing equipment and is thus very expensive. The line type printing equipment allows its printing heads to remain stationary to print a desired image on the printing medium which is conveyed and will thus be faster in the printing action and less noisy than the serial printing equipment.
As compared with the parallel printing equipment, the line type printing equipment has the following advantages and disadvantage.
The line type printing equipment has printing heads which are simpler in construction than those of the parallel printing equipment, so that the overall dimensions are small and the cost of production is low. Also, the printing speed of the line type printing equipment is equal to that of the parallel printing equipment. The line type printing equipment is however lower in resolution of prints on the printing medium than the parallel printing equipment.
Recently, for minimizing the overall size without sacrificing the printing speed, the color printer provided with the line type printing equipment is equipped with an improved device for conveying the printing medium.
A conventional color printer including the line type printing equipment which is more expensive than that with the serial printing equipment but less than that with the parallel printing equipment has been developed which is equal in printing speed, smaller in overall size, and slightly lower in the resolution of prints than that with the parallel printing equipment, and therefore, is now common for both business and personal uses.
For minimizing the overall size of a conventional color printer provided with the line type printing equipment without decreasing the printing speed, the device for conveying the printing medium includes a rotary drum having an outer surface thereof facing a plurality of printing heads of the line type printing equipment and a printing medium holding device for detachably holding the printing medium to the outer surface of the rotary drum with certainty. In action, while the rotary drum is rotated a number of times with the printing medium detachably held to its outer surface by the printing medium holding device, the printing heads print down a desired image of different color inks on the printing medium.
In order to increase the printing speed of the conventional color printer which comprises the line type ink jet printing equipment using the rotary drum as a printing medium conveying device of a small size, it is needed to increase a printing medium discharge speed of a printing medium discharge apparatus used for discharging the printing medium from the rotary drum after the desired image is printed on the medium.